Cardiac rhythm management system with intramural myocardial pacing leads and electrodes

ABSTRACT

Medical devices and therapeutic methods for use in the field of cardiology, cardiac rhythm management and interventional cardiology, and more specifically to catheter-based systems for implantation of pacing leads and electrodes, or intramural myocardial reinforcement devices, within the myocardial wall of the heart, such as the ventricles, to provide improved cardiac function.

DESCRIPTION OF THE INVENTION

This application claims the benefit of U.S. Provisional Application60/398,586 filed on Jul. 26, 2002.

FIELD OF THE INVENTION

The invention relates generally to medical devices and therapeuticmethods for their use in the field of cardiology, cardiac rhythmmanagement and interventional cardiology, and more specifically tocatheter-based systems for implantation of pacing leads and electrodes,or intramural myocardial reinforcement devices, within the myocardialwall of the heart, such as the ventricles, to provide improved cardiacfunction.

BACKGROUND OF THE INVENTION

In the normal heart, the electrical activity, which initiates thesubsequent mechanical contraction, is very organized. In general, onceone cell is activated, the adjacent cells of the heart will becomeactivated to propagate the electrochemical depolarization associatedwith systolic contraction of the heart muscle. Unlike skeletal muscle,each heart muscle is electrically connected to its neighbors. Thisactivation usually starts in the right atrium, in the sinoatrial node.From here, the electrical activity spreads across the right and leftatrium through either special conduction (i.e., faster pathways) orthrough normal atrial tissue. To electrically activate the main pumpingchambers of the heart, the left and right ventricles, the electricalactivity passes through the atrioventricular node. Within this node, thespread of electrical activity is relatively slow. Mechanically, thisallows the atrium to contract and pump blood into the ventricles beforethe ventricles contract.

Following this relatively slow spread of cardiac action potential, theelectrical activation travels rapidly down a special conduction pathway,known as the bundle of His. The bundle of His divides into right andleft bundle branches; the left dividing in turn into an anterior andposterior branch. This network consists of high-speed conduction fibers,known as the Purkinje fibers. From here, the remaining ventricularmuscle cells are activated. This high-speed network is essential for asynchronized contraction of each ventricle relative to associated atria,and for efficient, mechanical synchrony between the left and rightventricles.

Ischemic heart disease and other clinical problems (fibrosis, etc.) cancause conduction delays and/or blockage in this high-speed network. Forexample, a left bundle branch block leads to late electrical activationof the left ventricular free wall. These conduction problems change theQRS complex in the ECG to a wide QRS complex greater than 120 ms. Thecorresponding electrical conduction delays cause mechanical dysfunction,decreased cardiac output, as well as valvular regurgitation. Clinicalstudies have shown early septal circumferential shortening, followed bylate stretch as the left ventricular free wall shortenings begins(Kawaguchi M, Murabayashi T, Fetics B J, Nelson G S, Sarmejima H, NevoE, Kass D A. Quantitation of basal dyssynchrony and acuteresynchronization from left or biventricular pacing by novel-contrastvariability imaging. Journal of the American College of Cardiology 2002;39:2052-8). This electrical-mechanical dyssynchrony decreases cardiacoutput and may cause or exacerbate mitral regurgitation.

The electrical synchrony can be partially restored by biventricularpacing. A pacemaker is implanted in the patient along with a rightatrial, right ventricular, and left ventricular lead. The right atriallead is used to sense the electrical activity in the right atrium and/orto stimulate the right atrium. The pacemaker senses this electricalactivity and after a programmable delay (i.e., the delay can bedifferent for each ventricle) electrically stimulates the right and leftventricles, thereby re-establishing electrical synchrony. The leads canbe either bipolar or unipolar, and general consist of a coiledconductor, which is electrically isolated from the surrounding tissue.Numerous materials, such as platinum or tantalum coated MP35N alloywire, can be used for the conductor. At the distal end, the conductormakes electrical contact with the tissue via an electrode, commonly aring electrode. The electrode can elude an anti-inflammatorycortico-steroid, such as sodium dexamethasone, to reduce irritation oftissue adjacent to the electrode. Insulation materials such aspolyurethane, silicone, and ethylene tetrafluor ethylenefluoropolymerare used. The proximal end is directly connected to the pacemakerthrough an IS-1 standard connector with a sealing-ring (de Voogt W G,Pacemaker leads: Performance and progress. American Journal ofCardiology 1999; 83:187D-191D).

Initial clinical trials show that resynchronizaton therapy increasesexercise capacity and peak oxygen consumption, increases leftventricular ejection fraction, and decreases left ventricularend-diastolic size: all very positive changes for patients with heartfailure. These studies also indicate that left ventricular pacing may beas effective as biventricular pacing (Abraham W T, Fisher W G, Smith AL, Delurgio D B, Leon A R, Loh E, Kocovic D Z, packer M, Clavell A L,Hayes D L, Ellestad M, Messenger J. Cardiac resynchronization in chronicheart failure. New England Journal of Medicine 2002; 346:1845-53).

A major technical and clinical challenge associated with theseapplications concerns the issue of how to place a left ventricular freewall electrode. A typical location for this left ventricular lead is thelateral left ventricular free wall mid way between the base and apex(Auicchio A, Klein H, Tockman B, Sack S, Stellbrink C, Neuzner J, KramerA, Ding J, Pochet T, Maarse A, Spinelli J. Transvenous biventricularpacing for heart failure: can the obstacles be overcome? AmericanJournal of Cardiology 1999; 83:136D-142D.). A specialized leftventricular lead is placed into a distal cardiac vein by way of thecoronary sinus through a guiding catheter. For example, the EASYTRACKsystem (Guidant, St. Paul, Minn.) is a transvenous, coronary venous,unipolar pace/sense lead for left ventricular stimulation. [PurerfellnerH, Nesser H J, Winter S, Schwierz T, Hornell H, Maertens S. Transvenousleft ventricular lead implantation with the EASYTRACK lead system: TheEuropean experience. Am J Cardiol 2000; 86 (suppl):157K-164K.] The leadis delivered through a guiding catheter with a specific design tofacilitate access to the ostium of the coronary sinus. This catheterprovides pushability by incorporating an internal braided-wire design.The distal end of the catheter features a soft tip to prevent damagingof the right atrium or the coronary sinus. The EASYTRACK lead has a 6Fr. outer diameter and an open-lumen inner conductor coil that tracksover a standard 0.014-inch percutaneous transluminal coronaryangioplasty guidewire. The distal end of the electrode consists of aflexible silicone rubber tip designed to be atraumatic to vessels duringlead advancement.

In many patients (i.e., at least 10%), either the lead cannot be placedor complications (e.g., dissection or perforation of the coronary sinusor cardiac vein, complete heart block, hemopericardium, and cardiacarrest) occur (Abraham 2002). Because of these difficulties, the leftventricular lead is sometimes placed through a small thoracotomy(Auricchio A, Stellbrink C, Sack S, Block M, Vogt J, Bakker P, Huth C,Schondube F, Wolfhard U, Bocker D, Krahnefeld O, Kirkels H. Long-termclinical effect of hemodynamically optimized cardiac resynchronizationtherapy in patients with heart failure and ventricular conduction delay.Journal of the American College of Cardiology 2002; 39:2026-33.).

SUMMARY OF THE INVENTION

In accordance with the present invention, devices and methods areprovided for an effective intervention, which contemplates theimplantation of intramural, myocardial pacing leads and electrodes, aswell as implants for localized reinforcement of infarcted myocardialtissue, by delivery from the right ventricle directly into the leftventricular free wall.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one (several) embodiment(s) ofthe invention, and together with the specification serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a cross-sectional, planar view of the left and rightventricles with the distal end of a guide catheter wedged into thejunction of the right ventricular free wall and the interventricularseptum, to facilitate introduction and implanting of a pacing leadwithin the intramural myocardial tissue of the heart.

FIG. 1 b depicts an intramural pacing lead with multiple electrode sitesfor pacing.

FIG. 1 c illustrates multiple, intramural pacing leads implanted withinthe left ventricular myocardium.

FIG. 2 illustrates an implantable, intramural pacing lead which isintroduced along a curved trajectory to simplify introduction.

FIGS. 3 a-3 c illustrate several examples of pacing lead tips whichenhance echo-based imaging to facilitate placement.

FIG. 4 a illustrates the resistance forces associated with theendocardial or epicardial surfaces during lead/electrode introduction.

FIG. 4 b illustrates an exemplary pacing lead with a spherical shapedtip to enhance echo-based imaging and minimize likelihood of leadintroduction inadvertently piercing the epicardial tissue duringintroduction.

FIG. 4 c depicts an exemplary pacing lead having a shaped tip anddeflectable shaft to minimize forces exerted against the epicardialsurface during lead introduction.

FIGS. 5 a-5 d illustrate several exemplary anchoring elements for theintramural pacing lead/electrode system.

FIG. 6 a illustrates shaft designs for the intramural lead/electrodesystems.

FIG. 6 b illustrates an exemplary, reduced-profile lead design.

FIG. 6 c illustrates an exemplary design providing for an externalcoiled wire around the intramural lead.

FIG. 6 d illustrates an external coiled wire incorporated into the outerinsulator of an exemplary intramural lead.

FIG. 7 illustrates exemplary designs for a tapered pacing lead,including a distal feature to provide enhanced echo-based imaging andtracking.

FIG. 8 depicts two pacing leads, placed circumferentially andspaced-apart vertically, to enable a uniform current distributionthroughout the myocardium.

FIGS. 9 a and 9 b depict placement of a coil electrode segment of theleft ventricular lead located in the lateral wall close to the base ofthe heart, and a coil electrode segment of the right ventricular leadplaced by the apex of the heart.

FIG. 10 illustrates one possible configuration for the left ventricularlead.

FIG. 11 depicts an exemplary myocardial reinforcement device implantedwithin an anterior wall infarct with the proximal end of the deviceconnected to a lead.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Reference will now be made in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Introduction and placement of appropriate ventricular pacing leads andelectrodes are the subject of this application, as well as improvedmethods for introducing myocardial tissue reinforcement devices withinthe intramural space. It is believed that several problems associatedwith traditional introduction and placement of left ventricular pacingleads can be circumvented according to the present invention, whichprovides for placement of the lead directly into the intramural space ofthe left ventricular myocardium via right ventricular catheterintroduction.

FIG. 1 depicts a cross-sectional, planar, short-axis view of the leftand right ventricles. Using a novel technique, a guide catheter is firstintroduced via a vein (e.g., right external jugular vein) and advancedinto the right ventricle. The distal end of the guide catheter is wedgedinto the junction of the right ventricular free wall and theinterventricular septum. X-ray or echo-based imaging facilitates thiscatheter positioning. In this example, the guide catheter is placed bythe anterior surface, but the guide catheter can also be placed by theposterior surface. A straight pacing lead is pushed from the guidecatheter directly into the intramural tissues of the myocardium. Thepacing lead and electrode system is advanced well into the leftventricular free wall comprising the intramural tissues. In thisexample, an imaginary position designated in FIG. 1, indicated at a 0degree position, representing the ideal ventricular lead placement. Theright ventricular free walls intercept the left ventricle atapproximately 120 and 240 degrees. It is understood that most straightpacing leads are capable of reaching locations approximately 30 degreesaway from the 0 degree position. In many patients, the conduction delaysare not symmetrical between the anterior and posterior wall. If theposterior wall were activated first, then the pacing lead position, asdepicted in FIG. 1 a, is ideal.

FIG. 1 b illustrates an exemplary pacing lead providing multiple sitesfor intramural pacing. In between these pacing spots, the lead iselectrically isolated for the myocardium. At the pacing sites, the leadcan be provided with appropriately spaced-apart electrodes along itsdistal shaft which establish a direct electrical contact with themyocardium at desired locations. All the sites or selected sites can beused to re-establish electrical synchrony.

FIG. 1 c illustrates an exemplary anterior pacing lead within themyocardium. The guide catheter has been removed, and the lead has beenconnected to the stimulator. A second pacing lead can be similarlyplaced. The guide catheter is repositioned by the posterior junction ofthe septum and the right ventricular free wall. A straight pacing leadis advanced from the guide catheter into the posterior left ventricularfree wall.

FIG. 2 illustrates a cross-sectional, planar, short-axis view of theleft and right ventricles with the distal end of the guide catheterwedged into the junction of the right ventricular free wall and theinterventricular septum. In this example with a simple curve, the pacinglead is advanced well into the left ventricular free wall, well beyondthe 0 degree point. Thus with a simple curve, in this case similar tothe curvature of the left ventricular epicardial surface, the pacinglead is placed well into the left ventricular free wall.

Numerous methods are available to achieve a curved pacing lead. Forexample, if the distal portion of the pacing lead is straight, a curvedstylet inserted along its length can induce a curve in the distalportion of the lead. The curvature of the stylet can be selected tomatch the corresponding curvature of the heart. Guide wires have beendeveloped with a preferred shape or are steerable. U.S. Pat. No.5,769,796 issued to Palermo, for example, describes a super-elasticcomposite guidewire. This is a composite guidewire for use in a catheterand is used for accessing a targeted site in a patient's body. Theguidewire core or guidewire section may be of a stainless steel or ahigh elasticity metal alloy, preferably a nitinol-type of super-elasticalloy, also preferably having specified physical parameters. Thecomposite guidewire assembly is especially useful for accessingperipheral or soft tissue targets. Variations include multi-sectionguidewire assemblies having, in part, super-elastic distal portions andsuper-elastic braided reinforcements along the mid or distal sections.U.S. Pat. No. 5,480,382 issued to Hammerslag and U.S. Pat. No. 6,165,139issued to Damadian, for example, describe steerable guidewires. Incertain cases, a movable pull wire extends through the guide wire to itstip. Pulling on this wire causes the tip of the guide wire to bend.Similar approaches can be employed to steer a pacing lead.

Several imaging techniques are available (e.g., X-ray, MRI,echocardiography) to follow or track pacing lead placement. In cardiaccatheterization laboratories, for example, X-ray imaging is often usedto position catheters within the right ventricular chamber. The sameequipment and imaging can be used in the positioning of the pacing leadwithin the intramural space of the myocardium. For example, once thepacing lead is within the myocardial tissue, the relativecircumferential or base-to-apex direction of the guidewire advance canbe easily observed. The relative endo-to-epicardial positioning issomewhat more difficult to ascertain, but it can be inferentially orrelatively determined in response to the movement of the pacing lead inrelationship to the left ventricular cavity.

The positioning of the pacing lead into the left ventricular myocardiumcan also be guided by echocardiography. Ultrasound imaging,echocardiography, is widely available and provides excellentvisualization of cardiac structures. Echocardiographic guidance canfacilitate placing the lead. The echo images can help with thepositioning of pacing lead within the myocardium. In real time, the echoimages provide the exact positioning of these leads within themyocardium. This real time imaging makes placement of these leadseasier. Transthoracic and transesophageal echocardiographic views canalso be used.

The lead itself is made more visible under echo by having multiplesurface features to reflect the echo sound. A simple example of thissurface is the commonly used clinical braided or coiled guide wire. Onepotential difficulty with using echo guidance is to follow the tip ofthe pacing lead. The rest of the pacing lead must follow the tip, soknowledge of tip position is critical. A two-dimensional echo view takesa thin slice, in effect, across the left ventricle. With this thinslice, the tip of the pacing lead may move out of the field of view, andthus may not be easily recognized. FIG. 3 a, for example, depicts auniformly-shaped tip for a pacing lead. This shaped tip may be hard tofollow accurately under echo. Simple variations of this design aredepicted in FIGS. 3 b-3 c, to facilitate tracking. By having a known,different shape at the tip of the pacing lead, the exact position of thetip can be easily followed.

The pacing lead itself can be modified or altered to increases itsvisualization under echo. As described in U.S. Pat. No. 6,053,870,transverse notches in the lead increase the echo reflecting area, thusenhancing the ultrasound image. As described in U.S. Pat. No. 6,106,473,the lead can be coated with material to enhance its echogenicity. Thelead can also generate sound waves as described in U.S. Pat. No.5,967,991. A piezo-driver assembly is coupled to the lead, causing thetip to vibrate. These vibrations can be matched to the frequency of theechocardiographic transducer. (Armstrong G, Cardon L, Vilkomerson D,Lipson D, Wong J, Rodriguez L L, Thomas J D, Griffin B P. Localizationof needle tip with color doppler during pericardiocentesis: In vitrovalidation and initial clinical application. J Am Soc Echocardiogr 2001January; 14(1):29-37).

During placement, it is also possible to ascertain the relative positionof the pacing lead within the myocardium, based upon the inherent tissueproperty differences of the intramural space and boundary tissues of theepicardium. The actual resistance to pushing the pacing lead is verydifferent on the surfaces versus the interior of the myocardium, and thetactile feedback of the user will likely suffice to confirm the relativeposition is being maintained within the intramural space. FIG. 4 aillustrates these differences, and it can be appreciated that piercingor exiting the endocardial or epicardial surface requires more forcethan pushing the pacing lead through the interior myocardium.Consequently, these physical characteristics of the heart can be used tokeep the pacing lead within the myocardium. FIG. 4 b illustrates across-sectional view of the left ventricle, including a pacing lead witha spherical shaped tip introduced into the left ventricular free wall.The tip is being pushed against the epicardial surface. The angle atwhich the tip is being pushed against the epicardium and the sphericalshape of the tip create a very high force, which opposes the pacing leadfrom being pushed through the epicardium. The force or resistancedeflects the tip and keeps the pacing lead within the myocardium as thelead is advanced, as shown in FIG. 4 c. The pacing lead thus remainsjust below the epicardial surface as it is pushed around the leftventricular free wall.

Adjusting the strength or stiffness of the pacing lead can also assistthis restraining force. To accomplish this purpose, the ideal lead wouldincorporates two extreme functions, namely, being relatively stiff toprovide column strength along its length for pushing the lead into themyocardial tissue, while offering a relatively flexible or floppy distalsegment to avoid trauma to the epicardial surface and provide thedesired steering characteristics. By selecting the appropriate balanceof structural features and flexibility, the pacing lead can be advancedinto the myocardium with relatively modest prospect of inadvertentlyexiting through the epicardium or endocardium. The pacing leads willthus preferably have variable flexibility along the length of the lead.U.S. Pat. No. 6,146,339 issued to Biagtan, for example, describes aguide wire with operator controllable tip stiffness. Many differentapproaches are available to vary the stiffness of the pacing leads. Forexample, U.S. Pat. No. 5,957,903 issued to Mirzaee describes a guidewirewhose stiffness is adjusted by advancing or retracting a movable corewithin the guidewire.

The anchoring element comprises another important component of the leadsystem. Once the pacing lead is properly positioned, the anchoringelement is deployed to maintain the pacing lead in this position. FIGS.5 a-5 d illustrate several exemplary anchoring elements for theintramural pacing lead/electrode system. FIG. 5 d, for example, providesan anchoring element serving dual functions, namely, preventing thepacing lead from exiting the epicardium and keeping the lead in itsproper position within the intramural space of the myocardium.

FIGS. 6 a and 6 b illustrate alternative body designs for the leads.FIG. 6 a depicts a traditional design for a bipolar lead. An electricalinsulator separates two conductors, and both conductors are enclosedwithin an outer insulator. The conducting wire is not insulated. FIG. 6b depicts shows a design where both conducting wires are insulated andenclosed within an outer insulator, which offers a reduced profiledesign. As described above, however, these standard designs may be lesssuitable for the right ventricular placement of the left ventricularpacing lead, since their relatively smooth surfaces will not likelyimage well under echo techniques. Without distinctive features, it isbelieved that the distal end of the lead would be hard to follow duringplacement with echo guidance. More importantly, the stiffnesscharacteristics of these standard leads are not suitable to provide thecolumn strength necessary to advance the leads through myocardialtissues. As these leads are pushed through the tissue, resistance tofurther insertion increases until one portion of the lead buckles. Atthis point, the lead cannot be further advanced. Since these traditionalleads are not currently designed for applications of this type,modifications are believed necessary to minimize tissue irritation andthe build-up of scar tissue by the electrodes.

Therefore, a new lead design is required for the right ventricularintroduction and placement of the left ventricular lead within theintramural space of the myocardium. As described in U.S. Pat. No.6,106,473, the outer insulator of the lead is coated with material toenhance its tracking characteristics and echogenicity. FIGS. 6 c and 6 dshow additional surface features to increase the echogenicity of thelead. In FIG. 6 c, an external coiled wire is wrapped around the lead,which provides a lead that is more visible under echo (by having anechogenic coating and including multiple surface features to reflect theecho sound). In FIG. 6 d, an external coiled wire is incorporated intothe outer insulator of the lead. The outer insulator of the lead iscoated with material to enhance its echogenicity. This lead is morevisible under echo by having the multiple surface features to reflectthe echo sound and by the surface coating.

In connection to the leads described in FIGS. 6 c and 6 d, FIG. 7illustrates a relatively extended distal section of the lead. The distalend of the lead has a distinctive feature, which facilitates echotracking. In this example, the tip has a spherical shape. This shape canbe solid or a wire mess to reduce tissue trauma. In other designs,additional imaging-enhancing features can be employed, including thering electrode itself. Since the smooth metal surface of the electrodemay offer reduced echo visibility, a contrast can be incorporated in thedesign which better distinguishes the echogenic wire wrap part of thelead versus the echolucent electrode associated with the tip of thelead.

By selecting the appropriate lead strength or stiffness, the lead isable to be easily introduced into the intramural space, while posing areduced likelihood of inadvertently piercing epicardial or endocardialsurfaces. As shown in FIG. 7, for example, the thickness and relativestiffness of the leads desirably varies along the length of theelectrode to support steering through the myocardial tissue and provideconformity with the curved, ventricular free walls. The flexibility ofthe tip minimizes long-term trauma with the surrounding tissue,resulting in decreased scar formation by the electrodes, and thusproviding better long-term electrical pacing characteristics.

Other components of the pacing leads are constructed by standardtechniques known to those familiar with the arts. Numerous materials,such as platinum or tantalum coated MP35N alloy wire, can be used forthe conductor. At the distal end, the conductor makes electrical contactwith the tissue via an electrode, commonly a ring electrode. Theelectrode can elude an anti-inflammatory cortico-steroid such as sodiumdexamethasone to reduce irritation of tissue adjacent to the electrode.Insulation materials such as polyurethane, silicone, and ethylene tetrafluorethylenefluoropolymer are used. The proximal end is directlyconnected to the pacemaker through an IS-1 standard connector with asealing-ring.

In addition to the use of the above-described use of the presentinvention for support of cardiac resynchronization therapies, furtheradaptations of the present invention are contemplated for management ofother electrical stimulation therapies of heart tissue, such as cardiaccontractility modulating signals. Prolonging membrane depolarization byvoltage-clamp techniques applied to isolated cardiac muscle increasestrans-sarcolemmal calcium entry into the cell and thus enhancecontractility (Wood E H, Heppner R L, Weidmann S. Inotropic effects ofelectric currents. I. Positive and negative effects of constant electriccurrents or current pulses applied during cardiac action potentials. II.Hypotheses: calcium movements, excitation-contraction coupling andinotropic effects. Circulation Research 1969; 24:409-445.).Extracellularly applied electrical signals have a similar effect asvoltage clamping in muscles isolated from normal animals and failinghuman hearts. When applied regionally, electrical currents enhancecontractility of normal and failing hearts in-vivo (Mohrl S, He K L,Dickstein M, Mika Y, Shimizu J, Shemer I, Yi G H, Wang J, Ben-Haim S,Burkhoff D. Cardiac contractility modulation by electric currentsapplied during the refractory period. American Journal of Physiology2002; 282:H1642-H1647.).

While this concept of altering regional contractility has many potentialadvantages, there are currently several limitations presented whenconsidering traditional leads and electrode placement techniques. If theleads use ring-type electrodes, for example, the leads are in-effectonly point sources of the current, and only small regions of themyocardial will experience the positive contractility effects. Betterresults could be obtained by creating a larger electrical field, whichgenerally requires an electrode with a longer length. In addition to theelectrodes themselves, placement can be a problem. For most patients,however, left ventricular dysfunction or failure is the main problem.Thus, the leads need to be positioned within the left ventricle. Acatheter-based introduction approach (i.e., an intracardiac leadintroduced from the left ventricular cavity into the adjacent wall) candeliver these pacing electrode leads within the left ventricular cavity,which is believed to present a huge risk for thrombus formations andembolic clots. For external placement, a thoracotomy is required.

The same approaches described above can be employed to place leads inthe left ventricular free wall or septum via a catheter and withouttouching the left ventricular endocardial surface. FIG. 8 shows a viewof the left ventricular free wall. Embedded within the left ventricularmyocardium are two pacing leads, which are placed circumferentially, aspreviously described. In this illustration, one lead is placed closer tothe base, while the other lead is placed closer the left ventricularapex. The leads have either continuous or intermittent connection to themyocardium. In this example, the leads are placed around the entire leftventricular free wall. Partial coverage of the left ventricular freewall is also possible. By covering a broad area, the leads enable auniform current distribution over a larger portion of the leftventricle. The leads may optionally include intramural, myocardialelectrode implants that align with identified areas of myocardial tissuerequiring resynchronization or adjunctive pacing.

Ventricular fibrillation, chaotic electrical activity of the ventricularmyocardium, is a life-threatening event, if not treated quickly.Implantable defibrillators sense the heart's electrical activity anddefibrillate the heart when needed. Since the initial concept, the sizeand functionality of the implantable defibrillators have improved. Twodefibrillator issues still need to be resolved, namely, the size of thedefibrillators and the generated electrical field for defibrillation.While these issues may seem different, the issues are tied together. Themagnitude of the energy required to successfully defibrillate the heartwith a safety margin is a primary determinant of the implantabledefibrillators size. The leads used to distribute the defibrillationshock determine, in part, how much current will be needed.

Initially, pacing leads were placed external to the heart. Modern pacingsystems favor intracardiac leads, which are often transvascular, venousimplants. In one approach, the lead is placed in the right ventricleadjacent the endocardium, and the defibrillator itself constitutes theother lead electrode. The stimulator or pacing current is spread betweenthese two leads, such that it flows from the right ventricular lead tothe implantable defibrillator, which is often located in the pectoralregion. A disadvantage of this approach is the low current densitydelivered to the left ventricular apical region. Another approach, shownin U.S. Pat. No. 6,370,427 uses leads in both the left and rightventricular chambers. The shock current can be distributed between theright and left ventricular leads or between the leads and theimplantable defibrillator. Unfortunately, this approach fails to providean even current distribution, and also presents additional concernsrelating to potential lead thrombogenicity when placed directly withinthe left ventricular cavity.

By placing a lead within the left ventricular lateral wall close to thebase of the left ventricle, and positioning the other lead in the apicalright ventricle, a better current distribution can be achieved. In thisexample, both ventricular regions will receive appropriate cardioversionand defibrillator shock. FIGS. 9 a and 9 b, for example, show desiredlead positions. The coil electrode segment of the left ventricular leadis placed in the lateral wall close to the base. Placing the leftventricular lead within the myocardium further reduces the magnitude ofcurrent needed to successfully defibrillate the heart. The coilelectrode segment of the right ventricular lead is desirably placedwithin the right ventricular cavity by the apex. As described above, theleft ventricular lead is positioned just below the epicardial surface.This placement of the left and right ventricular leads provides animproved and more predictable current distribution across bothventricles.

This left ventricular lead can be placed from the right ventricle asdescribed for the resynchronization therapy, and can be used incombination with resynchronization therapy in an adjunctive manner. FIG.10 shows one possible configuration for the lead within the leftventricular myocardium. By selecting the appropriate lead strength orstiffness, the lead can be advanced into the myocardium with littlechance of exiting through the epicardium or endocardium. The thicknessand stiffness characteristics of the leads preferably vary along thelength of the electrode. The flexibility of the tip prevents the leadfrom penetrating the epicardium or the endocardium. The flexible tipalso minimizes long-term trauma with the surrounding tissues, and tendsto decrease scar formation by the electrodes, thereby ensuring betterlong-term electrical characteristics. The stiffer body component of theproximal portion of the lead enhances introduction into the myocardium.

The coil-shaped electrode can be made from a single wire, butmulti-filament wire is preferred. The coil-shape provides a largesurface area to reduce electrical resistance, and more effectivelydistributes current density along the desired myocardial regions of theheart. Platinum clad titanium, platinum clad tantalum, or platinumcoated MP35N wire can be used for the coil. The coil-shaped electrodeportion of the lead makes the distal end of the lead echogenic, thusmaking echo tracking during positioning easier. The electrode isconnected to a coil conductor, which carries the current from theconnector pin to the electrode. Insulation materials such aspolyurethane, silicone, and ethylene tetrafluor ethylenefluoropolymercan be used along the length of the lead. A conventional connector pinis used to attach the lead to the implantable defibrillator.

It is also recognized that the above-described technique for leadintroduction can be practiced to introduce discreet, implantable deviceswithin the myocardial wall to provide acute reinforcement of localizedventricular regions damaged by a recent myocardial infarction. Thesereinforcement devices can be placed into the anterior and posterior leftventricular wall, as well as the septum from a right ventricle, usingthe approaches described in this application for placement of LV pacingleads and intramural pacing electrodes. Again, the steerable catheter isplaced into the right ventricle rather than the left ventricle. Thecatheter is positioned against the septum and the guidewire is advancedinto the septum as far as desired into the left ventricular free wall.The remaining deployment of these reinforcement devices follows the samesteps as generally described above.

As shown in FIG. 11, the intramural reinforcement can also be used as anelectrical bridge across the infarct region. In this example, theimplantable device is placed across an anterior wall infarct. The end ofthe MyoMend device embedded in the normal lateral wall is in electricalcontact with the surrounding tissue. The body of the device isencapsulated with an insulator. The other end of the device is connectedto a lead, which in turn connects to a pacemaker. If electricalsynchronization therapy is needed, the left ventricular lateral wall canbe stimulated through the lead/electrode system.

It is also recognized that the above-described technique for introducingintramural pacing leads could be accomplished with the combination oftwo devices. A novel intramural guidewire and a separate intramuralpacing lead can be used. The guidewire would possess the featuresdescribed above and would be optimized for intramural navigation. Theguidewire would include all of the novel features for pacing andintramural anchoring described in sections above. The guidewire would beintroduced to the target intramural tissue first and the pacing leadwould be introduced second. The pacing lead and/or guidewire could be ofa solid or hollow design.

It is also recognized that a device similar to that shown in FIG. 11could be fabricated that would be an electro-active bridge. The devicewould be placed across the infarct region in a manner described above.The device would use the heart's systole deformation to store strainenergy and then convert this energy into electrical energy to bedischarged back to the distal end of the device at the next systoliccycle. This discharge would allow depolarization to spread to theopposite side of the infarct region that would otherwise be blocked. Thedevice could also have an electrical sensing circuit/system and logicwithin to better time the exact point of discharge.

Other embodiments of the invention will be apparent to those of skill inthe art from consideration of the specification and practice of theinventions disclosed herein. It is intended that the specification andexamples be considered as exemplary only.

What is claimed is:
 1. A method for direct localized therapeutictreatment of myocardial tissue in heart having a pathological conditioncomprising the steps of: a. identifying a target region of themyocardium having an epicardial region and an endocardial region and anintramural space defined between; b. delivering a lead having anelectrode to said intramural space; wherein said electrode is configuredto be connected to a therapeutic or diagnostic device, and wherein themechanical properties of at least a portion of the myocardial tissue ofthe target region substantially identified in step (a) is physicallymodified.
 2. The method of claim 1 wherein the modified mechanicalproperties include an increase in systolic performance.
 3. The method ofclaim 1 wherein the therapeutic or diagnostic device is a pacemaker. 4.The method of claim 1 wherein the therapeutic or diagnostic device is acardioverter/defibrillator.
 5. The method of claim 1 wherein thetherapeutic or diagnostic device is a cardiac resynchronization device.6. The method of claim 2 wherein the modified mechanical propertiesinclude substantially no decrease in diastolic performance.
 7. Themethod of claim 1, wherein said target region includes a myocardialinfarct or ischemic zone.
 8. The method of claim 7, wherein the leadincludes an electro active bridge for spanning said infarct or ischemiczone.
 9. The method of claim 1, wherein said delivering step furthercomprises delivering a substantially arcuately curved lead into theintramural space.
 10. The method of claim 9 wherein said delivering stepfurther comprises using a stylet.
 11. The method of claim 9 wherein saiddelivering step further comprises using a guidewire.
 12. The method ofclaim 1, wherein said lead further comprises echo features for aidingvisualization.
 13. The method of claim 1, wherein said lead furthercomprises radiopaque features.
 14. The method of claim 1, wherein saidlead further comprises a drug eluting surface.